Achim Hilgers, Eberhard Waffenschmidt, Philips Research
Magnetic induction works on alternating magnetic fields. To limit magnetic emissions and their impact on other devices or the user, detailed investigations during the design process are necessary.
Using simulation tools based on finite element methods (FEM) the most critical spots can be determined and evaluated.
The simulations show that the magnetic field decays very fast with increasing distance and critical areas are only very close to the device. Therefore, the size of the measurement sensor is very critical. Commonly used sensors with a diameter of about 10 cm integrate over a large area and may give results that hide the hot spots. To investigate possible effects on the user, simulations show details, which cannot be measured easily. Figure 12 shows a setup to determine the impact on a user’s hand in the vicinity of a mobile device by using an artificial hand model suitable for FEM calculations. The results show that for a typical setup as would be used for a mobile device, a power of 5 W can be transmitted without harm to the user.